The present invention relates to a semiconductor device in which a semiconductor chip generating heat is located between a pair of heat sinks and to a method for manufacturing the device.
A semiconductor chip for controlling large electric power and current generates so much heat in use that a proposed semiconductor device including the chip includes a pair of heat sinks, which are made of a metal such as copper and aluminum, to efficiently release the heat generated by the chip. As shown in FIG. 1, in a proposed semiconductor device 1, a semiconductor chip 2 and a coupler 5 are located between a first heat sink 3, or a lower heat sink 3, and a second heat sink 4, or an upper heat sink 4. The upper heat sink 4 and the coupler 5, the coupler 5 and the chip 2, and the chip 2 and the lower heat sink 3 are respectively connected by solders.
The upper and lower heat sinks 4, 3 also function as electrodes for the semiconductor chip. A mold resin 6 is located between the heat sinks 3, 4 to seal the chip 2, the coupler 5, and the solders. As illustrated in FIG. 1, the upper and lower heat sinks 4, 3 are respectively exposed on the lower surface and the upper surface of the device 1. Therefore, the upper and lower heat sinks 4, 3 efficiently transmit and release the heat generated by the chip 2 while being insulated partly by the mold resin 6.
As shown in FIG. 2, the semiconductor device 1 is located in use between a cooling member 7 and a U-shaped metal fixer 9, which is connected to the cooling member 7 by male screws 10. Two insulating sheets 8 are respectively located between the cooling member 7 and the device 1 and between the device 1 and the metal fixer 9. The cooling member 7 is made of a metal such as copper and aluminum, which can efficiently transmit and release heat. Although not illustrated, the cooling member includes a cooling water passage. The metal fixer 9 is made of a metal such as copper and aluminum. The insulating sheets 8 needs to be made of an insulating material that is thermally conductive and elastically shrinkable.
In the semiconductor device 1, the upper and lower heat sinks 4, 3 are exposed, so the insulating sheets 8 are needed to insulate the exposed surfaces and the metal fixer 9 is needed to transmit the heat generated by the chip 2 from the upper heat sink 4 to the cooling member 7. Therefore, the structure of the assembled article shown in FIG. 2 is relatively complicated, and the manufacturing cost of the assembled article is relatively high.
In addition, the thickness of the semiconductor device 1 deviates to some degree. Therefore, when the semiconductor device 1 is fixed to the cooling member 7 with the metal fixer 9, it is difficult to control the force with which the metal fixer 9 presses the device 1 against the cooling member 7. When the thickness of the semiconductor device 1 deviates too much from a predetermined value, the semiconductor device 1 breaks or is not firmly fixed to the cooling member 7. If only the insulating sheets 8 absorbed the force enough, the above problem could be solved. However, no material that is elastically shrinkable enough to be used for the insulating sheets 8 has been available yet.
Moreover, in the semiconductor device 1, the heat generated by the semiconductor chip 2 is partially transmitted from the upper heat sink 4 to the cooling member 7 through one of the insulating sheets 8 and the metal fixer 9. Therefore, the heat transmission path through the upper heat sink 4 is much longer than that through the lower heat sink 3, so the upper heat sink 4 releases the heat less efficiently than the lower heat sink 3.